Ryan f906be6bd9 Fixed Nullable value-type fields in Views in C# module causing excessive logging (#3949) ...

# Description of Changes

This PR fixes a C# codegen performance/behavior issue triggered by views
that include nullable value-type fields (e.g. `DbVector2?`), as reported
in #3914.

* Updated the C# BSATN code generator to emit non-boxing equality for
`Nullable<T>` members by using `System.Nullable.Equals(a, b)` rather
than `a.Equals(b)` (which can box and cause excessive host logging/work
in view diff/equality paths).

This causes code generation to change from something like:
``` csharp
// From:
var ___eqNullableIntField = this.NullableIntField.Equals(that.NullableIntField);
// To:
var ___eqNullableIntField = System.Nullable.Equals(
    this.NullableIntField,
    that.NullableIntField
);
```
* Added a regression scenario to the C# regression-test module that
exercises the problematic pattern:
  * A table containing a nullable struct field (`DbVector2? Pos`).
  * A public view that returns rows containing that nullable field.
* A reducer to mutate the nullable field from `some` → `none` → `some`
to force view re-evaluation and diffing.
* Updated the regression-test client to:
  * Subscribe to the new view.
* Validate that the view evaluates successfully and contains the
expected rows.
  * Call the reducer and validate view state after updates.
  * Fail the test if view evaluation/diffing produces errors.

# API and ABI breaking changes

None.
* No changes to public SpacetimeDB schema or wire format semantics.
* Changes are limited to generated equality code and regression tests.

# Expected complexity level and risk

2 - Low
* The codegen change is small and localized (special-casing
`System.Nullable<T>` equality generation).
* Risk is primarily around subtle behavior differences in equality for
nullable value types; however, `System.Nullable.Equals` matches the
expected semantics and avoids boxing.
* Regression tests specifically cover the nullable-struct-in-view
scenario to guard against regressions.

# Testing

<!-- Describe any testing you've done, and any testing you'd like your
reviewers to do,
so that you're confident that all the changes work as expected! -->

- [X] Ran the C# regression test suite via `run-regression-tests.sh` and
confirmed no errors.

2026-01-06 17:56:05 +00:00

..

snapshots

Fixed Nullable value-type fields in Views in C# module causing excessive logging (#3949)

2026-01-06 17:56:05 +00:00

client.csproj

Add C# diagnostics support (#1688)

2024-09-27 19:07:08 +00:00

Lib.cs

Rename Address to ConnectionId (#2220)

2025-02-10 00:40:16 +00:00